Facet joints are the hinge-like joints that connect vertebrae together. They are located at the back of the spine (posterior), and work alongside the vertebral discs to form a functional working unit of the spine. These joints help support the weight of the vertebra, and control movement between individual vertebrae of the spine, such as flexion, extension and twisting motions. In addition, the facet joints are synovial joints, which means each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. Cartilage coats the joint surfaces and allows the joints to move or glide smoothly against each other.
As with other bone joints, facet joints are almost constantly in motion with the spine, and are therefore susceptible to degeneration such as from osteoarthritis. Degenerative facet joint disease is a type of osteoarthritis that can cause the break down of the cartilage covering the facet joint surfaces, the result of which is joint inflammation-degradation in the spine that can lead to bone spurs or enlargement of the joints. The disease itself may be due to simple wear and tear associated with aging, or due to severe obesity. The predominant symptom is back pain on motion, particularly at the joint or joints where the condition is present. Other symptoms that can occur are swelling, reduced range of motion, and muscle weakness.
There is no known cure for spinal osteoarthritis. Current treatments focus on reducing pain and slowing down the disease progression. These treatments vary depending on the degree of joint damage but can include lifestyle changes, over-the-counter or prescription painkillers and physical therapy. Another common treatment is injection into the affected facets, such as with an anesthetic numbing agent for shorter-term results or a corticosteroid for longer-term results.
Like other bone joints that have degenerated, more invasive treatments such as surgery may be used in certain cases. It can be useful to immobilize the affected spinal motion segment in order to stabilize the spine as well as reduce the pain associated with motion of the damaged joint. This can be particularly applicable in the cervical spine, where chronic neck pain is prevalent in interventional pain management practices. Accordingly, it is desirable to provide implantable devices that are well suited for immobilization of diseased facet joints, and in particular cervical facet joints. The implantable devices should be easy to implant and provide structural integrity to the area to be treated. Even more desirable are implantable devices that also promote fusion of the damaged cervical facet joint in order to provide a longer-term solution to chronic neck pain.